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Kvardova et al. Molecular Cancer 2010, 9:147
http://www.molecular-cancer.com/content/9/1/147
Open Access
RESEARCH
The new platinum(IV) derivative LA-12 shows
stronger inhibitory effect on Hsp90 function
compared to cisplatin
Research
Veronika Kvardova1, Roman Hrstka1, Dawid Walerych2, Petr Muller1, Eva Matoulkova1, Veronika Hruskova3,
Dagmar Stelclova3, Petr Sova3 and Borivoj Vojtesek*1
Abstract
Background: Cisplatin and its derivatives are commonly used anti-cancer drugs. However, cisplatin has clinical
limitations including serious side effects and frequent emergence of intrinsic or acquired resistance. Thus, the novel
platinum(IV) complex LA-12 represents a promising treatment modality, which shows increased intracellular
penetration resulting in improved cytotoxicity in various cancer cell lines, including cisplatin resistant cells.
Results: LA-12 disrupts cellular proliferation regardless of the p53 status in the cells, however the potency of the drug
is greatly enhanced by the presence of a functional p53, indicating several mechanisms of action. Similarly to cisplatin,
an interaction of LA-12 with molecular chaperone Hsp90 was proposed. Binding of LA-12 to Hsp90 was demonstrated
by Hsp90 immunoprecipitation followed by platinum measurement using atomic absorption spectrometry (AAS). An
inhibitory effect of LA-12 on Hsp90 chaperoning function was shown by decrease of Hsp90-assisted wild-type p53
binding to p21WAF1 promoter sequence in vitro and by accelerated ubiqutination and degradation of primarily unfolded
mutant p53 proteins in cells exposed to LA-12.
Conclusions: To generalize our findings, LA-12 induced degradation of other Hsp90 client proteins such as Cyclin D1
and estrogen receptor was shown and proved as more efficient in comparison with cisplatin. This newly characterised
molecular mechanism of action opens opportunities to design new cancer treatment strategy profitable from unique
LA-12 properties, which combine DNA damaging and Hsp90 inhibitory effects.
Background
Cisplatin [cis-diamminedichloroplatinum(II)] is a platinum-based anticancer drug commonly used for treatment of different types of cancer, including ovarian,
testicular, head and neck or lung carcinomas [1].
Although cisplatin exerts significant anti-tumour activity,
cisplatin-based therapies cause numerous side effects,
such as nephrotoxicity, neurotoxicity and nausea. The
intrinsic as well as acquired resistances to cisplatin-based
therapy also represent substantial complications for the
treatment of tumours.
For this reason, vast efforts were committed to develop
novel platinum-based complexes to overcome platinum
resistance, to reduce cisplatin side effects and to introduce
* Correspondence: vojtesek@mou.cz
1
Department of Oncological and Experimental Pathology, Masaryk Memorial
Cancer Institute, Zluty kopec 7, 656 53 Brno, Czech Republic
novel mechanisms of anti-cancer action. Two derivatives,
carboplatin (cis-diammine-(1,1-cyclobutanedicarboxylato)platinum(II)) and oxaliplatin (trans-R,R.cyclohexane1,2-diammine)oxalatoplatinum(II)), have been introduced [2]. Taken together, these three drugs represent all
of the available platinum drugs approved by the Food and
Drug Administration for clinical use [3]. In addition to
substantial side effects, these three drugs also require
intravenous administration, therefore a new generation of
platinum drugs represented by satraplatin (JM216) [(OC6-43)-bis(acetato)amminedichloro(cyclohexylamine)platinum(IV)] has been generated. JM216 represents the first
orally administered platinum compound which has been
evaluated in clinical trials [2,4,5].
LA-12,
[(OC-6-43)-bis(acetato)(1-adamantylamine)amminedichloroplatinum (IV)], is a hydrophobic
platinum(IV) complex structurally similar to JM216,
Full list of author information is available at the end of the article
© 2010 Kvardova et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
Kvardova et al. Molecular Cancer 2010, 9:147
http://www.molecular-cancer.com/content/9/1/147
Results
Time and dose dependent accumulation of LA-12 in cancer
cells in comparison with cisplatin
LA-12 and cisplatin uptake into cells was determined by
AAS platinum amount measurement in lysates of cells
treated with different doses of these drugs for different
periods of time. We observed rapid and high initial accumulation of platinum after 0.5 hour incubation with LA12 in all concentrations used, rising up to 4 hours of incubation. In subsequent time points, platinum level
remained stable. The platinum amount in cells was also
dependent on the concentration used.
In contrast, there was no platinum detected in response
to 1 μM cisplatin treatment. Compared to LA-12 exposure, platinum levels were detected only when 10 μM and
50 μM cisplatin doses were administered. In response to
LA-12, platinum levels were 30 to 50 times higher
depending on concentration used and time interval (Figure 1). These results demonstrate that cellular uptake of
LA-12 is faster and more effective compared to cisplatin.
LA-12 specifically interacts with Hsp90
To assess the anticipated interaction of Hsp90 with LA12, we measured in triplicate the amount of platinum
bound to Hsp90 by AAS after immunoprecipitation of
Hsp90 from H1299 cells treated with 10 and 50 μM both
LA-12 and cisplatin. We detected significant amounts of
platinum after LA-12 treatment in contrast to cisplatin
treatment, where only after using 50 μM concentration
was a limited amount of platinum detected (about detection limit of AAS) (Table 1). The presence of Hsp90 in the
samples after immunoprecipitation was confirmed using
western blot (Figure 2). These data show that LA-12
4,5
4
log ng Pt/mg protein
which contains 1-adamantylamine instead of cyclohexylamine non-leaving ligand [6] which provides this drug
different properties. LA-12 has shown a higher cytotoxicity than JM216 when tested on a panel of 14 cancer cell
lines of various origin and different cisplatin sensitivity
[6,7] and no cross-resistance with cisplatin [6,8]. LA-12
has also displayed (i) higher antitumor activity in comparison with cisplatin and JM216, (ii) favourable pharmacokinetics and (iii) relatively low acute toxicity in a panel
of pre-clinical in vivo studies [9-11].
The cytotoxic mode of action of cisplatin is mediated
by its interaction with DNA to form DNA adducts, primarily intra-strand crosslink adducts, which activate several signal transduction pathways, including those
involving ATR, p53, p73, and MAPK, and culminate in
the activation of apoptosis [12]. JM216 has a mechanism
of action similar to that of cisplatin, inducing the formation of DNA adducts and inter- and intra-strand crosslinks and resulting in G2 arrest and induction of
apoptosis [13]. The principle mechanisms of LA-12
effects are not fully understood to date, although there is
some evidence that exposure to LA-12 can disrupt cell
proliferation and induce apoptosis more potently than
cisplatin in both p53 dependent and independent manners [14,15]. Interestingly, LA-12 induces unique changes
in the profile of gene expression compared to cisplatin,
indicating a distinct mode of action resulting in the differential activation of both p53-dependent and p53-independent gene targets [16].
Besides the well known cisplatin DNA-mediated effect,
the other mechanism of cisplatin action was described
demonstrating that cisplatin may also disrupt the function of some proteins, including heat shock protein 90
(Hsp90) [17]. According to this study, cisplatin associates
with the molecular chaperone Hsp90 and reduces its'
chaperone activity. For example, this can result in the
degradation of steroid receptors [18] and/or inhibition of
interaction between Hsp90 and inositol hexakisphosphate kinase-2 (IP6K2), which disrupts the inhibitory
effect of Hsp90 on IP6K2, leading to increased diphosphoinositol pentakisphosphate (IP7) formation and sensitisation of cancer cells to apoptosis [19,20].
Since it is supposed that LA-12 undergoes metabolic
changes and serves actually as a pro-drug for chemotherapeutically active platinum analogues, it is possible that
these active metabolites can interact with proteins analogous to cisplatin, resulting in stronger cytotoxic or cytostatic effects. According to this hypothesis we have
analyzed whether LA-12 can bind to Hsp90 resulting in
inhibition of its protective chaperoning function such as
folding, stabilization, activation and assembly of its "client" proteins.
Page 2 of 9
3,5
1 μM LA-12
3
10 μM LA-12
50 μM LA-12
2,5
1 μM cisplatin
10 μM cisplatin
2
1,5
50 μM cisplatin
1
0,5
0
0
1
2
3
4
5
6
7
8
9
time of incubation (hours)
Figure 1 Platinum accumulation in H1299 cells. H1299 cells were
treated with varying concentrations of LA-12 and cisplatin for indicated time intervals. Platinum levels in cell lysates were analysed by AAS.
Results are mean ± SD of triplicate experiments.
Kvardova et al. Molecular Cancer 2010, 9:147
http://www.molecular-cancer.com/content/9/1/147
Page 3 of 9
Table 1: Analysis of interaction of Hsp90 with LA-12
Sample
Applied
Result (± SD)
Result
compound
mg Pt/ml
ng Pt/mg protein
D-MEM
negative
-
10 μM cisplatin
10 μM cisplatin
2.09 (0.05)
50 μM cisplatin
50 μM cisplatin
9.93 (0.21)
10 μM LA-12
10 μM LA-12
1.96 (0.01)
50 μM LA-12
50 μM LA-12
9.14 (0.26)
L1
negative
-
L2
10 μM cisplatin
0.040 (0.0004)
20
L3
50 μM cisplatin
0.290 (0.005)
145
L4
10 μM LA-12
1.98 (0.02)
990
L5
50 μM LA-12
11.6 (0.26)
5500
P1
negative
-
P2
10 μM cisplatin
-
P3
50 μM cisplatin
< 0.02
P4
10 μM LA-12
0.034 (0.004)
P5
50 μM LA-12
0.222 (0.01)
NC1
50 μM cisplatin
-
NC2
50 μM LA-12
-
AC1
50 μM cisplatin
-
AC2
50 μM LA-12
-
Platinum levels were determined by AAS in whole cell lysates (L1-5) of H1299 control cells and cells treated with 10 μM and 50 μM LA-12 or
cisplatin for 9 hours. The protein concentration of cell lysates was 2 mg/ml. The amounts of platinum bound to Hsp90 was measured after
immunoprecipitation of Hsp90 from H1299 control cells and cells treated with 10 μM and 50 μM LA-12 or cisplatin for 9 hours (P1-5).
Immunoprecipitations without antibody (NC1-2) and with DO-1 antibody (AC1-2) in cells treated with 50 μM LA-12 and cisplatin were
performed as negative control for crossreactivity of platinum compounds with other reaction components. Control AAS platinum
measurements were perfomed in D-MEM cell medium containing 10 μM and 50 μM LA-12 or cisplatin. Results are mean ± SD of triplicate
experiments.
binds to Hsp90 more effectively than cisplatin in vivo,
probably due to the higher intracellular levels of LA-12.
Inhibition of Hsp90 assisted p53 binding to promoter
sequence of p21WAF1 by LA-12
The influence of LA-12 on the ability of wild-type p53 to
specifically bind to its target sequence derived from the
p21WAF1 gene promoter was tested using an electrophoretic mobility shift assay (EMSA). It is known that human
wild-type p53 binding activity is facilitated by molecular
chaperone Hsp90 under physiological conditions and this
process is inhibited by geldanamycin [21]. Thus in 22°C
wild-type p53 tetramers can bind to the p21WAF1 promoter independently of Hsp90 status. Under physiological conditions (37°C) in a control reaction without Hsp90,
human wild-type p53 loses its ability to bind to the
p21WAF1 promoter; however in presence of human
Hsp90β and ATP, wild-type p53 can develop transcriptionally active tetramers that bind to the p21WAF1 promoter sequence. In consequence, when Hsp90β is
inhibited by 17-AAG, the affinity of wild-type p53 to
p21WAF1 promoter is disrupted. Similarly, in a case of LA12 we also observed the disruption of Hsp90β activity
leading to inhibition of wild-type p53 DNA binding affinity (Figure 3). Cisplatin could not be effectively compared
to LA-12 and 17-AAG in this assay, as it directly disrupts
the p53 binding to promoter sequence (not shown).
LA-12 inhibits Hsp90 assisted folding and initiates
degradation of unfolded proteins
Hsp90 is important for folding and stabilization/degradation of client proteins. In our previous work we demon-
Kvardova et al. Molecular Cancer 2010, 9:147
http://www.molecular-cancer.com/content/9/1/147
Page 4 of 9
IgG
Mechanism of mutant p53 protein degradation in response
to LA-12
Control
10 μM Cisplatin
50 μM Cisplatin
10 μM LA-12
50 μM LA-12
Hsp90
strated that particular p53 mutations show different
ratios between native wild-type p53 conformations (recognized by PAb1620 antibody) and denatured conformations (recognized by PAb240 antibody) and highlighted
an important role of Hsp90 to maintain the mutant p53
protein conformation and stability [22]. In the case of
partially folded p53 mutants, such as R273H naturally
expressed in MDA-MB-468 cells, the native conformation is maintained by Hsp90. Thus, inhibition of Hsp90
results in a decrease of R273H mutant p53 folded conformation and an increase of denatured conformation,
although the overall protein levels are not changed. We
found that LA-12 is also able to cause the same changes
in R273H folded p53 mutant conformation without
appreciably affecting the level of total p53 protein (Figure
4A). In the case of predominantly unfolded mutant p53
proteins, such as R175H naturally expressed in SK-BR-3
cells, inhibition of Hsp90 function results in their degradation, and the identical effect is seen after treatment
with LA-12 (Figure 4B).
Lysate input
Hsp90
Actin
Immunoprecipitation
heavy chains
Figure 2 Detection of Hsp90 protein. The levels of Hsp90 protein in
H1299 whole cell lysates and after immunoprecipitation of Hsp90 in
LA-12 and cisplatin treated cells were analysed by western blotting.
EEV1-2.1 mouse monoclonal antibody was used for detection of Hsp90
protein.
A
In our previous work we have shown that naturally
unfolded mutants, such as p53 R175H in SK-BR-3 cells,
form stable complexes with chaperones and that Hsp90
activity is crucial to prevent their degradation [22]. If the
Hsp90 activity is blocked by 17-AAG, the denatured
mutants develop complex with Hsp70 and CHIP proteins, where ubiquitin ligase CHIP is responsible for
ubiquitination of unfolded p53 and ubiqutinated p53 pro-
B
1h, 22°C
-
22°C
37°C
1h, 37°C, Hsp90ß
DMSO LA-12 17-AAG
4%
200
100
DMSO
2%
2%
2%
4%
6%
LA-12
100
200
300
17-AAG
50
100
200
Figure 3 The Hsp90-dependent binding of wild-type p53 protein to p21WAF1 gene promoter sequence is inhibited by LA-12 and 17-AAG. A)
Wild-type p53 binding (0.125 μM tetramer) to the promoter sequence at 22°C (the main band) is not influenced by 4% DMSO (final concentration in
the reaction) or LA-12 and 17-AAG dissolved in the corresponding DMSO amount. B) Hsp90β (3 μM dimer) with 5 mM ATP (final concentration in all
reactions) rescues the p53 activity from inactivation at 37°C, in the presence of an increasing DMSO concentration, while LA-12 and 17-AAG inhibit
Hsp90β. The LA-12 stock solution is 2× more concentrated than 17-AAG to compensate for the lower LA-12 activity. Thus both inhibitors are in corresponding DMSO amounts: 100, 200, 300 μM LA-12 and similarly 50, 100, 200 μM 17-AAG introduce 2%, 4%, 6% DMSO concentration to the reaction,
respectively.
IP PAb1620
IP PAb240
Control
Cisplatin
LA-12
17-AAG
Control
Cisplatin
LA-12
17-AAG
Lysate input
Page 5 of 9
Control
Cisplatin
LA-12
17-AAG
Kvardova et al. Molecular Cancer 2010, 9:147
http://www.molecular-cancer.com/content/9/1/147
A) MDA-MB-468
B) SK-BR-3
Figure 4 Analysis of p53 mutant protein conformation. p53 mutant protein conformation was analysed in A) MDA-MB-468 cells containing mostly
folded p53 R273H mutant and B) SK-BR-3 cells containing only unfolded p53 R175H mutant. Cells were treated for 9 hours with 10 μM cisplatin, 10
μM LA-12 and 4 μM 17-AAG. Conformational changes of p53 were determined using immunoprecipitation with p53 conformation-specific mouse
monoclonal antibodies PAb1620 (detects folded conformation) and PAb240 (detects unfolded conformation). CM-1 rabbit polyclonal antibody was
used for detection of p53 protein.
tein is targeted for degradation in the proteasome [22,23].
To investigate whether LA-12 also initiates unfolded p53
mutant degradation via activation of CHIP ubiquitin
ligase, we compared mutant p53 levels in cells transiently
transfected by CHIP and a dominant-negative CHIP-TPR
truncated form, which contains the TPR domain (responsible for interactions with chaperones) but lacks the ubiquitination domain. In MDA-MB-468 cells with a partially
unfolded p53 mutant that is independent of Hsp90 activity, there was no effect of 17-AAG or LA-12 in the presence or absence of CHIP or CHIP-TPR (Figure 5A). In
mock-transfected SK-BR-3 cells, we observed a decrease
of mutant p53 in response to both LA-12 and 17-AAG, as
well as in cells transfected by CHIP. Importantly, transfection by CHIP-TPR decreased the rate of degradation
of the unfolded mutant p53, indicating the role of CHIP
ubiquitn ligase in degradation of R175H p53 mutant
caused by LA-12 (Figure 5B).
LA-12 induces degradation of not only mutant p53 but also
of other Hsp90 client proteins
Accordingly we found that LA-12 is responsible for massive decrease of p53 mutant proteins that adopt a predominantly denatured conformation (BT-474 and SK-BR3 cells); in cells which carry both native and denatured
conformations of mutant p53 (T-47D, BT-549 and MDAMB-468), the decrease of p53 level was noticeable only
after longer incubations (9 hours) with the drug. In
MDA-MB-231 cells, where mutant p53 occurs predominantly in native conformation, no decrease of p53 level
was observed even after prolonged incubation. Interestingly, apart from p53 protein, LA-12 also induces degradation of other Hsp90 client proteins, such as Cyclin D1
and Estrogen Receptor (Figure 6).
Importantly, the 10 μM drug dose used in our experiments is equal to 1.95 mg/l platinum, which corresponds
to the plasma levels of platinum shown in previous in vivo
studies [10,24]. The maximum platinum plasma concentration 1.54 and 6.25 mg/l in rats was observed within 1
hour after oral administration of 38.6 and 540 mg/kg LA12, respectively [24]. Interestingly, maximum tolerated
single oral dose of LA-12 in mouse model was 1000 mg/
kg [10].
Discussion
Platinum(IV) complexes represent a class of anticancer
agents that are activated by reactions with reducing
agents present in body liquids after their administration.
Thus, the platinum(IV) complexes display potential
advantages over their platinum(II) counterparts because
of their greater stability and bioreductive activation,
thereby allowing a greater proportion of the drug to
arrive at the target intact. Thus, it is not surprising that
the cellular uptake of LA-12 was faster and more effective
than that of cisplatin (Figure 1).
Hsp90 is a molecular chaperone and is one of the most
abundant proteins expressed in cells [25]. Molecular
chaperone Hsp90 is a member of the heat shock protein
family, which is up-regulated in response to stress and its'
in vivo function is ATP-dependent [26]. Hsp90 exists as a
homodimer, which contains three domains. The N-terminal domain contains an ATP-binding site that binds the
natural products geldanamycin and radicicol. Hsp90
function depends upon the ability of the N-terminal
domain to bind and hydrolyze ATP, which is regulated
and coupled with the conformational changes of the
Hsp90 dimer [27]. The middle domain exhibits high
affinity for co-chaperones as well as client proteins [28].
Kvardova et al. Molecular Cancer 2010, 9:147
http://www.molecular-cancer.com/content/9/1/147
Page 6 of 9
B) SK-BR-3
17-AAG
LA-12
Cisplatin
17-AAG
Control
Cisplatin
LA-12
Control
LA-12
17-AAG
mock transfected CHIP transfected CHIP-TPR transfected
Control
LA-12
17-AAG
Cisplatin
Control
17-AAG
LA-12
Cisplatin
Control
17-AAG
LA-12
Cisplatin
Control
mock transfected CHIP transfected CHIP-TPR transfected
Cisplatin
A) MDA-MB-468
p53
CHIP
Actin
Figure 5 Analysis of p53 mutant protein degradation. p53 mutant protein levels were analysed in A) MDA-MB-468 cells containing mostly folded
p53 R273H mutant and B) SK-BR-3 cells containing unfolded p53 R175H mutant transfected with CHIP or CHIP-TPR protein by western blotting. Cells
were treated for 9 hours with 10 μM cisplatin, 10 μM LA-12 and 4 μM 17-AAG. CM-1 rabbit polyclonal antibody and CHIP-11.1 mouse monoclonal
antibody were used for detection of p53 and CHIP proteins. Actin was used as loading control.
The structure of the C-terminus of Hsp90 contains the
MEEVD sequence, which is known to bind co-chaperones that contain multiple copies of the tetratricopeptide
repeat (TPR), a 34 amino acid sequence [29]. Interestingly, the middle C-terminal part of Hsp90 has been
implicated biochemically as the site of a putative second
cryptic ATP-binding site on Hsp90 [26]. The contribution
of this site to the overall regulation of chaperone function
is not clear, but novobiocin has been reported to interact
with this site and alter the conformation of the chaperone
[30]. Importantly, cisplatin has also been found to bind to
an Hsp90 site that overlaps the putative ATP/novobiocin
binding site in this region, leading to inhibition of some
Hsp90 activities [17,26]. The observed higher affinity of
Hsp90 to LA-12 may be explained by very specific properties of C-terminal domain of Hsp90. This domain contains several solvent-exposed hydrophobic residues,
which are responsible for binding of client protein such as
unligated glucocorticoid receptor [31]. Consequently the
hydrophobic properties of LA-12 could explain its preferential binding to Hsp90 in contrast to cisplatin.
The ability of LA-12 to inhibit Hsp90 function was
shown using several approaches. (i) EMSA, based on the
fact that under physiological conditions the chaperone
activity of Hsp90 is important for the transcriptional
activity of genotypically wild-type p53 [21] clearly demonstrated LA-12 as potent inhibitor of Hsp90 chaperon-
ing function. (ii) Determination of p53 conformation in
cells expressing various p53 mutants, which were
exposed to LA-12, revealed that the unfolded mutant p53
proteins that do not rely on Hsp90 activity are less stable
than folded mutant p53 proteins that require Hsp90
activity. These findings are in agreement with previous
work showing that the half-life of p53 mutant positively
correlates with their conformational stability [22].
It was shown that inhibition of Hsp90 results in ubiquitination and degradation of primarily unfolded p53
mutants. This MDM2-independent degradation of
unfolded p53 mutant is mediated by chaperone interacting protein CHIP. Our results show that CHIP is responsible for LA-12 mediated degradation in the same way as
17-AAG, which supports our theories finding LA-12 as a
specific Hsp90 inhibitor.
Accordingly to both higher cellular uptake of LA-12
and at least 10-fold higher presence of platinum bound to
Hsp90 in cells exposed to LA-12 compared to cells
treated by cisplatin (Table 1), a stronger suppressive
effect of LA-12 on Hsp90 activity and function in relation
to cisplatin could be expected. This statement was confirmed by the ability of LA-12 to influence the stability
and degradation rate of other Hsp90 client proteins, such
as estrogen receptor and cyclin D1 compared to cisplatin,
which did not decrease the level of these proteins.
Kvardova et al. Molecular Cancer 2010, 9:147
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Page 7 of 9
SK-BR-3
p53
CD1
CD1
ER
Actin
Actin
BT-549
T-47D
p53
LA-12
Cisplatin
Control
LA-12
Cisplatin
p53
CD1
CD1
Actin
ER
MDA-MB-231
p53
Actin
LA-12
Control
LA-12
Cisplatin
Control
LA-12
Cisplatin
LA-12
Cisplatin
Control
BT-474
p53
Cisplatin
3 hours 6 hours 9 hours
3 hours 6 hours 9 hours
CD1
MCF-7
p53
Actin
CD1
MDA-MB-468
p53
ER
CD1
Actin
Actin
Figure 6 Analysis of degradation of Hsp90 client proteins. Protein levels of p53, cyclin D1 (CD1) and estrogen receptor (ER) were determined in
cells treated for 3, 6 and 9 hours with 10 μM cisplatin and 10 μM LA-12 by western blotting. CM-1 rabbit polyclonal antibody, SP1 rabbit monoclonal
antibody and CD1 mouse monoclonal antibody was used for detection of p53, ER and CD1 proteins, respectively. Actin was used as loading control.
Conclusions
In summary, our data indicate that cellular uptake of LA12 is more effective compared to cisplatin resulting in
more extensive binding of LA-12 to Hsp90 in vivo. This
interaction is responsible for direct inhibition of Hsp90
chaperone function. These unique properties predict LA12 as a novel promising anti-cancer therapeutic exploit-
ing dual mode of action in inducing genotoxic damage
and inhibiting Hsp90 activity.
Methods
Cell cultures
All human cancer cell lines were obtained from ATCC.
Cell lines BT-474, MDA-MB-468, MDA-MB-231, T-47D,
Kvardova et al. Molecular Cancer 2010, 9:147
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BT-549 and SK-BR-3 contain different p53 mutations
(E285K, R273H, R280K, L194F, R249S and R175H,
respectively), whereas the wild-type allele was lost in all
these cell lines. MCF-7 cells contain wild-type p53, and
H1299 cells are p53-null. Cells were periodically checked
for morphology by microscope and regularly screened for
mycoplasma using Hoechst staining.
Cells were cultured in Dulbecco's Modified Eagle's
Medium (DMEM) (Invitrogen, Paisley, Scotland) supplemented with 10% fetal bovine serum (Invitrogen, Paisley,
Scotland), 300 mg/l L-glutamine (Invitrogen, Paisley,
Scotland), 100 U/ml penicillin (Invitrogen, Paisley, Scotland) and 0.1 mg/ml streptomycin (Invitrogen, Paisley,
Scotland), in a humidified incubator at 37°C in 5% CO2
atmosphere. Cells were grown to 80% confluence prior to
experimental treatments.
Chemicals
Page 8 of 9
[33,35]. For immunoprecipitation of Hsp90 protein for
platinum amount measurement by AAS, cells were lysed
in 150 mM NaCl, 50 mM HEPES (pH 7.2) and 0.5%
Tween 20 and sonicated. Protein concentrations were
measured using Bradford's assay. 200 μl of cell lysate containing 400 μg of total protein was incubated overnight
together with 2 μg of EEV2-1.1 mouse monoclonal antibody against Hsp90β protein (in house antibody) and
AC88 mouse monoclonal antibody against Hsp90 protein
(Stressgen Biotech Corp., Victoria, BC, Canada). 15 μl of
G-protein sepharose beads (GE Healthcare, Wien, Austria) was used to precipitate the antibody. After three
washes in lysis buffer, beads were resuspended in 200 μl
of 150 mM NaCl, 50 mM HEPES (pH 7.2) and 0.5%
Tween 20 and boiled for 10 min.
Preparation of samples for AAS platinum amount
measurement
The following anti-neoplastic drugs were used in this
study: LA-12, cisplatin (Pliva-Lachema a.s., Brno, Czech
Republic), 17-AAG (Alexis Biochemicals, Lausen, Switzerland). LA-12 and cisplatin were dissolved in DMSO
and diluted in cell medium to 0.5 mM stock solution and
17-AAG was dissolved in DMSO to 2 mM stock solution.
Stock solutions of LA-12 and cisplatin were freshly prepared before use. The final concentration of DMSO in
cell culture medium did not exceed 0.2%.
Cells were incubated for the given time intervals with different doses of LA-12 and cisplatin. Control and treated
cells were collected by centrifugation, washed three times
with ice-cold PBS, lysed in 150 mM NaCl, 50 mM HEPES
(pH 7.2) and 0.5% Tween 20 and sonicated. Protein concentrations were measured using Bradford's assay. 200 μl
of cell lysate were used for platinum amount measurement by AAS.
SDS-PAGE and western blotting
Human wild-type p53 and human Hsp90β were purified
and activity of p53 was quantified by EMSA as described
previously [36]. Simplified, the assay is based on the ability of human recombinant Hsp90 to restore the specific
DNA binding activity of human recombinant p53 at 37°C
in vitro. A preincubation with Hsp90 inhibitors prior to
p53 inactivation at 37°C was carried out as described for
geldanamycin [21].
SDS-PAGE and western blotting were performed as
described previously [16]. The following antibodies were
used: DO-1 mouse monoclonal antibody directed
towards the epitope 20-SDLWKL-25 within the p53 N-terminal region [32], CM-1 rabbit polyclonal antibody
against human p53 protein (in house antibody), CHIP11.1 mouse monoclonal antibody recognizing full length
as well as truncated CHIP protein (in house antibody),
Estrogen Receptor (clone SP1) rabbit monoclonal antibody (Lab Vision, Fremont CA, USA), CD1 mouse monoclonal antibody recognizing Cyclin D1 (in house
antibody), EEV1-2.1 mouse monoclonal antibody against
Hsp90 protein (in house antibody) and AC-40 monoclonal antibody recognizing actin (Sigma-Aldrich Inc. St.
Louis, USA), which was used as a protein loading control.
Final concentration of all antibodies used for immunodetection of proteins was 1 μg/ml in 5% milk containing
0.1% Tween 20 in PBS.
Immunoprecipitation
Immunoprecipitation of conformationally different forms
of p53 protein was performed using 1 μg of mouse monoclonal antibodies PAb1620 recognizing the wild-type
conformation of human p53 protein at native form
[33,34] and PAb240 recognizing the mutant conformations of p53 at native form [35], as described previously
In vitro p53 DNA Binding Assay
List of abbreviations
AAS: Atomic absorption spectrometry; EMSA: Electrophoretic mobility shift assay; CHIP: Carboxy terminus of
Hsp70-interacting protein; MDM2: Mouse double minute 2 homolog; Hsp90: Heat shock protein 90
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
VK designed, performed and analysed platinum accumulation experiments,
performed immunoprecipitation experiments and prepared the manuscript,
RH designed and performed degradation experiments and prepared the manuscript, DW performed EMSA experiments, EM performed CHIP transfection
experiments, VH and DS performed AAS analysis, PM and PS contributed to the
experimental design of the study, BV contributed to the conception and
design of the entire study and the final editing of the manuscript. All authors
read and approved the manuscript.
Acknowledgements
We thank Dr. P. J. Coates for critical reading of the manuscript. This work was
supported by PLIVA-Lachema a. s., IGA MZ CR NS/9812-4, MZ0MOU2005 and
GACR 301/08/1649.
Kvardova et al. Molecular Cancer 2010, 9:147
http://www.molecular-cancer.com/content/9/1/147
Author Details
1Department of Oncological and Experimental Pathology, Masaryk Memorial
Cancer Institute, Zluty kopec 7, 656 53 Brno, Czech Republic, 2Department of
Molecular Biology, International Institute of Molecular and Cell Biology in
Warsaw, 4 Ks. Trojdena Street, 02-109 Warsaw, Poland and 3Research and
Development, PLIVA-Lachema a.s., Karásek 1, 621 33 Brno, Czech Republic
Received: 11 March 2010 Accepted: 15 June 2010
Published: 15 June 2010
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doi: 10.1186/1476-4598-9-147
Cite this article as: Kvardova et al., The new platinum(IV) derivative LA-12
shows stronger inhibitory effect on Hsp90 function compared to cisplatin
Molecular Cancer 2010, 9:147